Update to 3.28

Upstream changes:
2013-05-04  David E. Wheeler <david@justatheory.org>
* Release 3.28

Removed use of 'done_testing' in t/white.t, which was added in
v3.27. Thanks to Paul Howarth for the catch.

Fixed inproperly calculated number of skipped tests in t/xhtml01.t
when HTML::Entities is not intalled.

2013-05-03  David E. Wheeler <david@justatheory.org>
* Release 3.27

Added new warnings as defined by Pod::Checker, thanks to RJBS:
+ "=over" without "=back"
+ "L<>" starts or ends with whitespace
+ raw "|" or "/" in "L<text|link>" text

Added ->keep_encoding_directive, which is false by default, to
prevent formatters from emitting a document's '=encoding'
directive in most cases. That they emitted the encoding was a bug
introduced in v3.26 (RT #84093). Now, only the DumpAsText and
DumpAsXML formats set it to true. Patch from Patrice Dumas.

2013-02-27  David E. Wheeler <david@justatheory.org>
* Release 3.26

Fixed another test script to skip all tests when Encode is not
installed.

Added 'encoding()' and 'detected_encoding()' to return the current
encoding and the encoding actually to decode the input file. The
value from "=encoding" is also now kept in the output tree. Patch
from Patrice Dumas (RT #74390).

(wen)